Well, I agree that for the sake of reconciling YOUR marriage, telling the OP's spouse is usually harmful (in that your WAS will likely resent it).
BUT - as the cheated-upon spouse, I would have WANTED to be told. Not only for health reasons (if my spouse is catting around, I want to be able to protect myself from sexually transmitted diseases) but also for the sake of making informed life decisions (if I knew my husband was cheating, would I want to make another baby with him? Would I buy a new house with a big mortgage?)
Most people don't want to tell the cheated-upon spouse because they fear that person will turn on them. It's true - it often happens that they don't appreciate the bearer of bad news. But what if you KNEW that their spouse had contracted AIDS? Wouldn't you then feel it was your duty to warn them?
I guess, like many things, it depends on the situation. If you KNEW, for instance, that the OM ONLY slept with your wife, was remorseful, and that your wife did not have any STDs .... then a reasonable argument might be made for not telling his wife, if there are children involved and a family to preserve.
On the other hand, if you KNEW the OM was picking up prostitutes and having unsafe sex - I don't know how your conscience would enable you to keep that a secret from her.
The one thing you have to be careful of, though, is the revenge motive. Many LBSs want to tell the OPs spouse out of revenge - kind of "he messed up MY marriage, now I'm going to mess up HIS". Nothing good ever comes from a revenge motive.
